The migrant crisis engulfing Europe is likely to last for 20 years, the government minister in charge of Britain's international response warned on Thursday.

Justine Greening, the Secretary of State for the Department for International Development, said the humanitarian crisis in Syria was such that many refugees would be unlikely to return home in two decades.

It came as the European Union predicted that the worst of the crisis is yet to come, with three million people arriving by the end of 2017. It said the economic boost many had hoped for is likely to be negligible.

Ms Greening, whose department is in charge of Britain's £1.1bn aid package to Syria, spelt out the scale of the problem as new figures emerged from the European Union that dwarf previous estimates of the scale of the crisis.

Ms Greening said that Britain and other countries that have agreed to take in Syrian refugees now had to realise that the crisis would take decades rather than years to be resolved.

"In the 1980s, the typical time that someone spent as a refugee from conflict was about eight years, whereas today that estimate is around 20 years," she said.

"Therefore it is not good enough just to provide food and water and refugee camps where people can live.

"If people are going to be refugees for 20 years, they need good education for their kids and a job and livelihood for themselves. It is clear now that unless we support them to do that, they will take a longer term choice, which is to leave the region for good."

The European Commission said that another 1.5 million people could be expected to arrive in 2016, compared to one million this year, plus a further 500,000 in 2017 – increasing Europe’s population by 0.4 per cent.

The influx is putting “considerable strains” on countries and resulting in “political and social tensions”.

Contrary to the hopes of some German politicians, the analysis – part of the EU’s routine economic forecasting – said the arrival of asylum seekers would do little to boost the continent’s economy.

On the upside, the introduction of hundreds of thousands of young people will boost the labour force and partially offset the continent’s ageing population.

However, the report points out that refugees are less likely to find work than economic migrants, which have formed the basis for previous economic studies. Those in the current wave appear to have low skills and could face a wait to enter the jobs market due to their asylum status. Refugees tend to take the lowest-paid jobs and in the long-run have a lower employment rate than economic migrants.

“Labour-market outcomes thus crucially depend on how quickly and how well refugees are integrated,” the report said.

In the short-term, handling the arrivals will have a cost to the public purse of as much as 0.5 per cent of GDP in the most affected countries such as Sweden, greater than the immediate economic dividend.

Overall in Europe, the influx could increase the size of the continents’ economy by a quarter of one per cent. However, this is smaller than the population increase, “implying a small, negative impact on GDP per capita throughout the period”.

In Germany, growth is expected to increase by 0.5 per cent to 2020, against a population increase of one per cent “reflecting also stronger downward pressure on real wages.”

In recognition of this, Jean-Claude Juncker, the European Commission president, has called for a review of EU asylum rules to allow refugees to start working as their cases are processed.